1. Field of the Invention
The present invention relates to a photoelectric sensor and an emitting device for the photoelectric sensor. More particularly, the present invention relates to an improvement in structure of a photoelectric sensor having a transparent plate for passing through detection light and a casing holding an optical element irradiating or receiving the detection light, such as a photoelectric element or an emitting element.
2. Description of Related Art
Some photoelectric sensors have an optical element such as a photoelectric element and an emitting element; a main casing holding the optical element; a transparent plate coupled to the main casing; and for passing through a light related to the optical element. Japanese Laid-Open Patent No. 2001-155597 shows a structure for affixing the transparent plate to the main casing with a slide action.
According to conventional technology shown in the Japanese Laid-Open Patent, a sealing member such as a gasket is not installed between the main casing and the transparent plate which can slide on the main casing so as to be affixed on the main casing. Therefore, liquid, i.e. water and oil, is likely to leak in the main casing through a gap between the main casing and the transparent plate. The leakage is likely to damage the sensor.
For example, in the case where the sensors are installed in a product line, oil utilized in a processing machine may spread on the sensors. Then, the oil is likely to leak into the sensors. If the sensors installed in the product line fail due to the leakage of the oil, the operation of the product line is generally suspended until the failed sensors are replaced. This suspended time of the product line causes lower productivity. Moreover, even though the suspended time may be short, safety confirmation for restarting the product line may take a longer time. Thus, suspension of the product line causes reducing productivity.
Ring gaskets might be installed at the surroundings of the openings which are covered by a transparent plate so as to avoid leaking of liquid inside of the sensor. However, since the opening shape depends on the size of the sensor, various sizes of gaskets should be prepared in accordance with the size of the sensor. In the case of a multi-axis photoelectric sensor, the sensor should be prepared for various detection lengths so as to comply with various applications. So, in situation, the main casings of the sensors are made by cutting longitudinal pipe to desirable length. In this manner, it's easy to produce sensors having various detection lengths. But since the shape of the gasket is a ring, the above manner can not be adapted for producing the ring gaskets. Therefore, various sizes of ring gaskets should be prepared corresponding to the desire lengths of the main casings. Consequently, productivity is reduced.
One might consider using adhesive tape that is bonded along the opening instead of the gasket where a transparent plate is held by the adhesive tape. However, it may be difficult to place the adhesive tape between the main casing and the transparent plate because of the structure for sliding the transparent plate on the main casing to unit each other.